Facebook (FB - Get Report) , Alphabet (GOOGL - Get Report) and Twitter (TWTR - Get Report) are on the hot seat this week. 

Top lawyers for the tech giants are set to be grilled by Congress on how Russian actors allegedly used their platforms to try to influence the 2016 U.S. presidential election. The first hearing is set for Tuesday at 2:30 PM EDT in front of the Senate Judiciary Committee. Two additional hearings are scheduled for Wednesday -- the first in front of the Senate Select Committee on Intelligence at 9:30 a.m. ET and another at 2:00 p.m. ET in front of the House Intelligence Committee's Russia Investigative Task Force. All the hearings will be live streamed to the public

Top tech executives are expected to be absent from the hearings, but Facebook CEO Mark Zuckerberg and COO Sheryl Sandberg will likely face some questions from analysts about Russian meddling when the pair host the company's third-quarter earnings call on Wednesday at 5 p.m. ET. Don't expect to hear testimony from Google CEO Sundar Pichai or Twitter CEO Jack Dorsey, either.

Representing the tech giants are Facebook general counsel Colin Stretch, Twitter general counsel Sean Edgett and Google general counsel Kent Walker. 

Ahead of the hearings, Facebook, Twitter and Google have all released some evidence of Russian meddling on their respective platforms, but the companies are expected to tell Congress that the interference was more widespread than originally estimated. Facebook is expected to inform Congress on Tuesday that 126 million Americans may have viewed content from the Internet Research Agency (IRA), the Russian troll farm that ran at least 470 Facebook accounts and purchased 3,000 political ads -- totaling $100,000 -- during the 2016 election. And Twitter will tell lawmakers that as many as 36,746 IRA-linked accounts generated 1.4 million tweets during the presidential election. 

Earlier this month, Google disclosed that accounts linked to the Russian government had purchased $4,700 worth of ads. The company found an additional $53,000 worth of ads were bought from accounts with Russian internet addresses and Russian currency.

Facebook and Twitter have also taken preliminary steps to self-regulate ad disclosures, pledging to be more transparent about who is buying political ads on their platforms. Facebook is now requiring buyers of election-related ads to include a "paid for by" disclosure, while Twitter added new disclosure rules and is banning ads from Russian outlets Russia Today and Sputnik. Google has yet to introduce new disclosure rules. 

Senators have also authored a bill, called the Honest Ads Act, that would require online political ads to disclose their funding sources and archive all political ads sold above certain thresholds. Republican Sen. John McCain has already signed onto the bill, alongside co-authors and Democratic Sens. Amy Klobuchar and Mark Warner. 

In addition, on Tuesday, the Internet Association, a Washington, D.C.-based lobbying group that counts Google, Twitter and Facebook as members, released a series of principles on how online ads should be regulated. Among the recommendations, the group said that the Federal Election Commission should put in place uniform regulations that require all ad platforms to report disclosures, not just a few. It also argued that regulators should improve the transparency of political ads without discouraging free speech. 

So far, Facebook, Google and Twitter have adopted similar stances on Russian meddling on their platforms by promising to take the issue seriously. The response is likely to be different during this week's hearings, however, as tech firms go further than just telling lawmakers what they're currently doing to thwart Russian ad buying, said Ryan Hagemann, director of technology policy at the libertarian think tank the Niskanen Center.

"Eventually, they're going to have to start working more closely with lawmakers," Hagemann said. "We're going to see Washington pushing a lot harder on Silicon Valley, through legislation and political messaging." 

Tech firms have pledged to work more closely with legislators, but so far have stopped short of endorsing proposed regulations such as the Honest Ads Act. 

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